This application Application DE 100 63739.6 filed Dec. 21, 2000.
1. Technical Field
The invention relates to a substrate with at least one self-cleaning surface, the substrate is preferably a glass, ceramic, plastic or metal substrate, or a glazed or enamelled coated substrate. The self-cleaning surface located on the substrate is based on a coating located on the substrate, the coating forming a structure, and the surface structure configured to have elevations and depressions. Further, the surface is at least partly hydrophobic. The invention also relates to a composition for the production of a substrate with at least one self-cleaning surface, and to a process for the production of the same. The process includes coating the substrate with the abovementioned composition or coating. The invention also relates to various uses of a substrate having a self-cleaning surface.
2. Description of Related Art
To achieve both a good self-cleaning effect on a surface having a good level of hydrophobicity there must be a micro rough surface structure on the surface of a substrate. Both features (micro rough and hydrophobicity) are realized in nature, for example, in the lotus leaf. The surface of the lotus leaf has a hydrophobic material and pyramid shaped elevations that are a few xcexcm from one pyramid tip to another pyramid tip. Drops of water substantially contact only with the tips or peaks of the pyramids so that the contact area of water to surface is minuscule relative to the water drops contacting a micro smooth surface. The reduced surface area results in a very low adhesion between the water drops and the micro rough surface. The relationship of micro rough surfaces and hydrophobicity, and the applicability of the xe2x80x9clotus effectxe2x80x9d on surfaces, is taught by A. A. Abramzon, Khimia i Zhizu (1982), no. 11, 38 40.
Without reference to the LOTUS EFFECT(copyright), U.S. Pat. No. 3,354,022 discloses water repellent surfaces having a micro rough structure with elevations and depressions and a hydrophobic material. In particular, a fluorine containing polymer is disclosed as the hydrophobic material. According to one embodiment, a surface with a self-cleaning effect can be applied to ceramic brick or glass by coating the substrate with a suspension comprising glass beads and a fluorocarbon wax. The beads have a diameter in the range from 3 to 12 xcexcm. The fluorocarbon wax is a fluoroalkyl ethoxymethacrylate polymer. Unfortunately, such coatings have a disadvantageously low abrasion resistance and only a moderate self-cleaning effect.
European Patent No. EP 0 909 747 A1 discloses a process for producing a self-cleaning property of a surface. The method relates particularly to the surface of roof tiles. The surface has hydrophobic elevations having a height of 5 to 200 xcexcm. Such a surface is produced by application of a dispersion of powder particles of an inert material in a siloxane solution, and subsequent curing the siloxane solution to form a polysiloxane. Unfortunately, the structure forming particles are not well fixed to the surface of the substrate in an abrasion stable manner and thus the abrasion resistance is undesirably low.
European Patent No. EP 0 772 514 discloses a self-cleaning surface for objects with a synthetic surface structure having elevations and depressions. The distance between the elevations is in the range of from 5 to 200 xcexcm, and the height of the elevations is in the range from 5 to 100 xcexcm. The structure includes hydrophobic polymers, or materials that have been hydrophobized in a stable manner. Etching, embossing, and coating processes are suitable to form the structure. If necessary, the formation of the structure can be followed by a hydrophobization step, for example a silanization process.
Structured surfaces with hydrophobic properties are disclosed in European Patent No. EP 0 933 388 A2. The surfaces have elevations with an average height of 50 nm to 10 xcexcm and an average separation of between 50 nanometers (nm) to 10 micrometers (xcexcm), and a surface energy of the non structured material of 10 to 20 micronewtons per meter (mN/m). To achieve a particularly low surface energy, and thus hydrophobic and oleophobic properties, the structured surface includes fluorine containing polymers or has been treated using alkylfluorosilanes.
German (DE) Patent Application 100 16 485.4 discloses glass, ceramic and metal substrates having a self-cleaning surface. The surface has a structured and at least partly hydrophobized coating. The coating includes a glass flux and structure forming particles with an average particle diameter in the range from 0.1 micrometers (xcexcm) to 50 micrometers (xcexcm). The glass flux and structure forming particles are present in a volume ratio in the range from 0.1 to 5. The micro rough surface structure has a ratio of average profile height to average distance between adjacent profile peaks in the range from 0.3 to 10. The self-cleaning surface has a higher abrasion resistance relative to the self-cleaning surfaces of roof tiles disclosed hereinabove.
The present invention provides a substrate, and preferably a glass, ceramic, plastic, metal and/or glazed or enamelled substrate, with a self-cleaning surface. The self-cleaning surface preferably has a low roll off angle or high contact angle (and therefore a good self-cleaning effect), and is also transparent. The self-cleaning surface preferably has a very high contact angle with respect to water, preferably a contact angle of about/above 150xc2x0.
Subjecting the substrate to a hydrophobating process according to the present invention preferably does not reduce the transparency of a transparent substrate, such as glass or plastic. Additionally, a decorated surface subjected to a hydrophobating process according to the present invention, where the decoration is under the self-cleaning surface, is preferably clearly detectable by an observer of the surface. Glass, ceramic, and metal substrates, or glazed or enamelled substrates, preferably have a higher abrasion resistance relative to known hydrophobic substrates, in particular with reference to a structured surface that is made of an organic polymer, or that includes structure-forming particles bonded using an organic polymeric material. Additionally, the substrates with the self-cleaning surface according to the invention are preferably formed using a simple process. A preferred process is similar to processes used in the glass and ceramics industry or metal processing industry for decorating surfaces. These and further objects such as are deduced from the further description do not have to be achieved together in all the embodiments.